1. Field of the Invention
The present invention relates to an image forming apparatus for displaying an image output from a computer or the like, and more particularly, it concerns such apparatus in which a developer is electrostatically attached to a recording medium to form an image.
2. Description of the Related Art
The above-described type of image forming apparatus has been proposed in, for example, the specifications of U.S. Pat. Nos. 3,879,737, 3,914,771, 4,268,598 and 4,573,061. In the image forming apparatus described in those patents, developing agent 108 as shown in FIG. 6A is concentrated on recording electrodes 101 (FIG. 6B) by concentrating the magnetic flux of a magnetic field generated by an inner rotary magnet member 104 on the recording electrodes 101 by virtue of the presence of a magnetic member 102 made of a magnetic material. The magnetic member 102 is provided on a developing sleeve 105 that constitutes an outer cylindrical member surrounding the rotary magnet member 104. One end portion of the magnetic member 102 is located on the outer side of the developing sleeve 105 and extends in the radial direction thereof.
Further, the developing agent 108 supplied onto the developing sleeve 105 is reserved in a container 106, as shown in FIG. 6A. The amount of developing agent 108 supplied is restricted by a wall-shaped member 107 that forms part of the container 106.
In the above-described apparatus, the group of electrodes 101, together with the magnetic member 102, must be fixed to the outer cylindrical member of the developing sleeve 105. Accordingly, it is very difficult to manufacture a group of electrodes that can cope with an image having an extended width. In order to concentrate the magnetic flux, the magnetic member 102 has to be elongated in the radial direction of the developing sleeve 105, and a supporting member 110 must be provided on the sides of the magnetic member 102 in order to ensure mounting strength and the adherence of the electrodes, as shown in FIG. 6B.
Further, it is impossible to prevent the developing agent from flowing out through the ends of a gap formed between the electrodes and an associated recording medium at the location where the distance between the electrodes and the recording medium is the shortest.